Promoted absorbents for the removal of contaminants

ABSTRACT

A process for the removal of trace metals from a hydrocarbon stream includes contacting the hydrocarbon stream with an absorbent material comprising antimony pentoxide supported on an absorbent substrate. The hydrocarbon product is then withdrawn from the absorbent material to provide a purified product in which 99.5 wt. % of the trace metal has been removed. Preparation of the antimony pentoxide-promoted absorbent entails treating a particulate porous substrate with an aqueous solution of antimony pentoxide. The absorbent substrate has an average particle size within the range of 1-5 mm and an average pore volume within the range of 0.7-0.85 cubic centimeters per gram. At least 80% of the surface area of the support is contained within the internal pore volume of the absorbent. The absorbent support is contacted with the antimony pentoxide solution. Once the solution has been applied to the support, the mixture is agitated to ensure even distribution of the antimony pentoxide in the internal pore volume of the support. The antimony pentoxide support is then dried at an elevated temperature.

FIELD OF THE INVENTION

[0001] This invention relates to promoted absorbents and theirpreparation and more particularly to antimony pentoxide-promoted porousabsorbents and their preparation and use in the removal of metalcontaminates from hydrocarbon products.

BACKGROUND OF THE INVENTION

[0002] The presence of even trace amounts of metals such as copper andiron in hydrocarbon products can be highly deleterious. An example isfound in metal contaminated middle distillate fractions, such as fueloils involving kerosene, jet fuel, and diesel fuel. Contaminates, suchas small amounts of copper and iron, can be present in such hydrocarbonfractions from a number of sources. For example, in the purification ofhydrocarbon fractions designated for use as a jet fuel or as a dieselfuel, copper and/or iron-based catalysts can be used to remove offensivethiohydrocarbons, such as mercaptans, to produce a product stream of a“sweetened” hydrocarbon fuel. Subsequent to the sweetening process, theproduct stream can be subjected to an absorption procedure to removetrace amounts of copper and iron from the hydrocarbon fuel. A suitableabsorption process can involve passing the sweetened product streamsthrough a bed of an absorbent which absorbs the contaminated copper orother metal from the stream. An aluminum silicate absorbent, such asattapulgite, bentonite, kaolinite, halloysite, or the like, may be used.In addition to an aluminum silicate clay absorbent, large porealuminosilicate zeolites, such as zeolite Y, may also be used to absorbtrace metals from the stream.

SUMMARY OF THE INVENTION

[0003] In accordance with the present invention, there is provided aprocess for the preparation of a promoted absorbent effective for theremoval of metal contaminants from hydrocarbon products. In carrying outthe invention, there is provided a porous absorbent substrate in whichthe predominant surface area is contained within the internal porevolume of the substrate material. The absorbent substrate is contactedwith a solution of an absorption-promoting agent to provide a mixture ofthe absorbent substrate with the solution of promoting agent to at leastpartially fill the internal pore volume of the substrate with thesolution of promoting agent. The mixture of the particulate substrateand the promoting agent solution is agitated for a time sufficient toeffect distribution of the promoting agent within the internal porevolume of the absorbent support material. Thereafter, the supportsubstrate is contacted with a solution of the promoting agent in anamount, when added to the solution of promoting agent previouslyapplied, to provide an amount of the promoting agent solution which isat least equal to the pore volume of the porous absorbent substrate.This mixture is agitated for time sufficient to effect distribution ofthe promoting agent within the internal pore volume of the supportmaterial, and the absorbent substrate material is then dried at atemperature sufficient to dehydrate the substrate material with thepromoting agent in place. The promoting agent is an oxide of a metal ofGroup 15 (new notation) of the Periodic Table, which metal comprisesantimony or the Group 15 metals adjacent to antimony, specificallyarsenic or bismuth. Preferably, the Group 15 metal is antimony.

[0004] In a preferred embodiment of the invention, there is provided aprocess for the preparation of an antimony pentoxide-promoted absorbent.In carrying out the invention, a particulate porous absorbent substrateis treated with an aqueous solution of antimony pentoxide, typicallyhaving an antimony pentoxide concentration of about 10 wt. % or more.The porous absorbent substrate has an average particle size within therange of 1-5 mm and an average pore volume within the range of 0.7-0.85and preferably within the range of 0.75-0.8 cubic centimeters/gram. Atleast 80% of the surface area of the support is contained within theinternal pore volume of the absorbent. The absorbent support iscontacted with the antimony pentoxide solution, or sol, in an amountequal to or in excess of the pore volume of the porous absorbentsupport. The treating solution can be applied to the porous absorbentsupport in a single treatment, but preferably the treating solution isapplied in at least two stages. Whenever multiple application stages areemployed, after the initial stage, the mixture of the particulateabsorbent and the antimony pentoxide solution is agitated in order toeffect a distribution of the antimony concentration within the porevolume of the support. Thereafter, the absorbent material can becontacted in one or two additional stages with the antimony pentoxidesolution in a total amount, including the initial step, equal to or inexcess to the pore volume of the porous absorbent support material. Theabsorbent material is then dried at an elevated temperature sufficientto dehydrate the support.

[0005] In a further aspect to the present invention, there is provided aprocess for the removal of a trace metal, such as copper or iron, from ahydrocarbon product contaminated by the trace metal. In carrying outthis aspect of the invention, the hydrocarbon product is contacted withan absorbent material comprising antimony pentoxide supported on anabsorbent substrate. The hydrocarbon product is then withdrawn from theabsorbent material to provide a purified hydrocarbon product in which atleast 99.5 wt. % of the trace metal in the feedstock is removedproviding a final product having a trace metal content of no more than0.5 wt. % of the trace metal content of the feed product. In a preferredembodiment of the invention, the trace metal comprises copper such asmay be present due to a sweetening process carried out over a coppercatalyst. Preferably the substrate material is a fired attapulgite claywith a water content of about 5.0 wt. % or less.

[0006] The purified product preferably exhibits a copper content ofabout 0.03 ppm or less, as indicated by experimental work describedbelow. The copper content of the purified product may be reduced to avalue down to about 0.01 ppm, and it is preferred in carrying out theinvention to provide a copper content within the range of about0.01-0.03 ppm over a prolonged portion of use of the promoted absorbent.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007]FIG. 1 is a bar graph illustrating copper concentrations resultingfrom batch treatments of kerosene employing unpromoted clay and claypromoted with Sb₂O₅, H₃PO₄, and K₄P₂O₇.

[0008]FIG. 2 is a graph illustrating the copper concentration plotted onthe ordinate versus the time on stream plotted on the abscissa for ahydrocarbon stream passed over an antimony pentoxide-promoted absorbent.

[0009]FIG. 3 is a graph of copper concentration plotted on the ordinateversus time on stream plotted on the abscissa for a hydrocarbon treatedwith an unpromoted absorbent.

[0010] As noted previously, a preferred absorbent involves attapulgiteclay, and the invention will be described with respect to attapulgiteclay, which has been dried to a water content of 5 wt. % or less.

[0011] Antimony pentoxide is only sparingly soluble in water and thesolution or sol employed in carrying out the present invention isactually a colloidal dispersion of antimony pentoxide. Antimonypentoxide may be prepared by any suitable procedure which typically willinvolve the reaction of an antimony component, such as elementalantimony metal or antimony trioxide, with hydrogen peroxide to producecolloidal antimony pentoxide as disclosed in U.S. Pat. No. 4,348,301 toCrompton et al, U.S. Pat. No. 5,008,036 to Crompton et al, and U.S. Pat.No. 5,213,785 to Fentress et al. Typically, antimony trioxide isslurried in water in the presence of a stabilizer and contacted with anaqueous solution of hydrogen peroxide under controlled temperatureconditions to arrive at a relatively concentrated sol of antimonypentoxide. The conversion of the antimony trioxide to antimony pentoxidemay be carried out in either batch-type or continuous operations. For afurther disclosure of the suitable techniques for formation of colloidaldispersions of antimony pentoxide, reference is made to theaforementioned U.S. Pat. Nos. 4,348,301, 5,008,036, and 5,213,785, theentire disclosures of which are incorporated herein by reference.

[0012] In experimental work respecting the present invention, anincipient wetness technique was employed to promote an attapulgiteclay-based absorbent with antimony pentoxide and potassiumpyrophosphate. Preparation of the promoted absorbents involved using theincipient wetness impregnation (IWI) technique to deposit the promotersonto a granular clay support provided by fired attapulgite clay having aresidual water of hydration of about 2 wt. %. Prior to the wetting step,the granular clay support was sifted with a No. 30 W. S. Tyler sieve toremove fine clay particles. The resulting clay support had an averageparticle size of between 1 mm and 5 mm. The antimony pentoxide (Sb₂O₅)promoted clay was prepared by impregnation with an aqueous Sb₂O₅ sol.

[0013] The Sb₂O₅ sol was prepared in a similar fashion to the methodsdisclosed in the aforementioned patents to Fentress et al and Compton etal by the reaction of 103 grams antimony trioxide (Sb₂O₃) powder wettedwith 3 wt. % ethylene glycol, with 72 grams of 35% hydrogen peroxide(H₂O₂) (equivalent to about 2.2 moles of H₂O₂/mole of Sb₂O₃). Prior tothe addition of the H₂O₂, an aqueous stabilizer solution was added tothe aqueous Sb₂O₃ slurry (103 grams Sb₂O₃ powder, 87 grams H₂O). Thestabilizer solution consisted of 27.2 grams of 75% phosphoric acid(H₃PO₄) and 89.9 grams of triethanolamine (TEA). After the stabilizersolution was added to the Sb₂O₃ slurry, a thermometer was placed intothe slurry and the beaker was placed on a stir plate. The 35% H₂O₂solution was added slowly to the Sb₂O₃ slurry so as to maintain thereaction temperature below 180° F. Once the reaction was complete, thewhite slurry turned to a clear solution containing 29 wt. % Sb₂O₅.

[0014] Prior to impregnation of the Sb₂O₅ onto the clay granules, theSb₂O₅ sol was diluted in order to provide a volume sufficient to achievethe wetness point of the support with Sb₂O₅ loading within the range ofabout 10-15 wt. %. By starting with approximately 200 grams of dried andsifted clay granules (wetness point of clay support=0.78 cm³ liquid/gramof clay), it was necessary to use about 156 cm³ of Sb₂O₅ sol tocompletely saturate the pore volume of the support. By adding 80 cm³ ofpure H₂O to 75 cm³ of 29% Sb₂O₅ solution, sufficient liquid having anSb₂O₅ concentration of about 14.0 wt. % was provided to fill the poresof the support. The wetting step involved depositing the liquid solutiononto the clay support in three steps with extensive mixing betweenliquid treatment steps to insure even distribution of Sb₂O₅. Once theimpregnation was complete, the promoted clay was dried in a convectionoven at 350° F. for about 2 hours.

[0015] The preparation of H₃PO₄ promoted clay involved wettingapproximately 300 grams of dried and sifted attapulgite clay with anaqueous solution of phosphoric acid (H₃PO₄). A commercially available75% H₃PO₄ solution was diluted to 20% H₃PO₄ to provide sufficient liquidvolume to reach the wetness point of the clay. 234 cm³ of 20% aqueousH₃PO₄ was added in three steps with extensive mixing in between. Afterwetting, the sample was dried at 350° F. for about 2 hours.

[0016] The K₄P₂O₇ promoted clay was prepared using the IWI technique asdescribed previously for the Sb₂O₅ and H₃PO₄ promoted samples. Toachieve 10 wt. % K₄P₂O₇ loading on the clay, 32.7 grams of K₄P₂O₇ weredissolved in 255 cm³ H₂O to provide sufficient liquid volume to wet 327grams of the dried and sifted clay granules. After dissolving the K₄P₂O₇into the H₂O, the solution was added to the clay support in three stepswith mixing in between each step. Once mixing was complete, the samplewas dried in the oven at about 350° F. for around 2 hours.

[0017] Batch analysis experiments were carried out involving placingequal volumes of absorbent (promoted and unpromoted clay) and keroseneinto a volumetric flask and sealing with a stopper. Once sealed, theflask was placed into a heated water bath and the contents heated fromroom temperature to the temperature of the bath. Batch experiments wereperformed on Sb₂O₅ promoted clay, H₃PO₄ promoted clay, K₄P₂O₇ promotedclay, and unpromoted clay. In each of the experiments, approximately 90cm³ of kerosene, containing about 25 ppm (by weight) of copper wasplaced into a 250-mL volumetric flask with approximately 90 cm³ ofabsorbent. Once the flask was sealed, it was placed into a water bath at100° F. Periodically (about every 5 minutes), the contents in the flaskwere swirled to allow for intimate contact between the kerosene and theabsorbent. After 30 minutes, the flask was removed from the water bathand the kerosene was separated from the absorbent via gravityfiltration. After filtration, the sample was retained for residualcopper analysis. An induced coupled plasma (ICP) technique was used toanalyze the samples for residual copper.

[0018] Flow experiments were conducted in 2 quartz tube reactors (½ inchO.D.) connected in series. The kerosene was transported from a 1-Literflask to the reactors via a variable flow mini-pump. Heat was suppliedto the reactors via heating tape, which was connected to a solid-statepower controller with adjustable output. The temperature was monitoredvia two digital thermometers equipped with thermocouples, which wasplaced directly between the heating tape and outside of the quartz tubereactors. The temperature was maintained at approximately 150° F. forall of the flow experiments. Each reactor was able to hold approximately20-25 cm³ of absorbent giving a total absorbent volume of around 50 cm³.The kerosene flow to the reactors was adjusted to yield a liquid hourlyspace velocity (LHSV) ranging from 1.5-2.0 hr⁻¹. The samples obtainedfrom the product stream were collected approximately every 2-3 hours andwere subsequently subjected to residual copper analysis.

[0019] The results of the batch experiments are shown in FIG. 1 in whichthe bar graphs indicate the comparison between the different absorbentson the removal of copper from the kerosene. As shown in FIG. 1, theSb₂O₅ promoted clay was more efficient in the removal of copper fromkerosene than either unpromoted clay, H₃PO₄ promoted clay, or K₄P₂O₇promoted clay.

[0020] As noted previously, the initial copper concentration of theuntreated kerosene was 25 ppm (wt. %). After treating the kerosene withSb₂O₅ promoted clay, the copper concentration was reduced to 0.03 ppm,corresponding to a removal of 99.9% of the copper from the sample. Asindicated by the data in FIG. 1, the Sb₂O₅ promoted absorbent is muchmore efficient in the removal of copper from kerosene than either of theother promoted absorbents or the unpromoted clay which removed 98.8 wt.% of the copper from the kerosene.

[0021] The flow experiments were carried out with the unpromoted clayand Sb₂O₅ promoted clay absorbents following the protocols describedpreviously. The Sb₂O₅ promoted absorbent was exposed to kerosenecontaining 24.9-ppm copper for about 35 hours and exhibited efficientcopper removal for the entire run. The results are shown in FIG. 2 ofcopper concentration in weight parts per million plotted on the ordinateversus time on stream (TOS) in minutes on the abscissa. With theexception of the first sample, every treated kerosene sample analyzedfor no more than 0.03-ppm copper. This corresponded to removal of 99.9%of the initial copper present in the kerosene. The average LHSV for theexperimental work with the Sb₂O₅ promoted clay was 1.96 hr⁻¹, equivalentto processing approximately 3400 cm³ of kerosene over 49 cm³ ofabsorbent.

[0022] The same flow experiment was carried out on the unpromoted clay.The results are shown in FIG. 3 where the copper concentration (ppm) isplotted on the ordinate versus time on stream (TOS) in minutes on theabscissa. As shown in FIG. 3, the unpromoted clay did an acceptable jobin removing the copper in the kerosene for an initial period of time.However, after approximately 29.6 hours, a substantial increase in thecopper concentration of the treated kerosene was observed.

[0023] The average LHSV for the experiment performed on the unpromotedabsorbent was 1.67 hr⁻¹. Under this flow condition, the copper“breakthrough” occurred when approximately 2500 cm³ of kerosene had beenprocessed over the absorbent. This is significant because when comparedto the Sb₂O₅ promoted absorbent, after processing approximately 3400 cm³of kerosene at a higher LHSV (1.97 hr⁻¹), no copper “breakthrough” wasobserved.

[0024] By analysis of the foregoing experimental work, it is evidentthat the Sb₂O₅ promoted absorbent is more efficient in the removal oftrace metals, such as copper, from liquid hydrocarbon fuels, thanunpromoted clay, H₃PO₄ promoted clay, and K₄P₂O₇ promoted clay. TheSb₂O₅ promoted absorbent is highly effective for trace metals removal inliquid hydrocarbon streams.

[0025] While a preferred application of the present invention is in thepreparation of antimony pentoxide promoted absorbents, the incipientwetness technique described herein can also be used to establishpromoted absorbents based upon arsenic and bismuth. Thus, the incipientwetting technique can be employed to distribute a compound such asbismuth pentoxide or arsenic pentoxide within the internal pore volumeof a porous absorbent substrate.

[0026] Having described specific embodiments of the present invention,it will be understood that modifications thereof may be suggested tothose skilled in the art, and it is intended to cover all suchmodifications as fall within the scope of the appended claims.

What is claimed:
 1. A process for removal of copper from acopper-contaminated hydrocarbon product comprising, (a) contacting saidcontaminated hydrocarbon product with an absorbent material comprisingantimony pentoxide supported on a porous absorbent substrate; and (b)withdrawing said hydrocarbon product from said absorbent substrate toprovide a purified hydrocarbon product in which at least 99.5 wt. % ofthe copper content of the feed product has been removed.
 2. The processof claim 1 wherein said substrate material is an absorbent clay.
 3. Theprocess of claim 2 wherein said absorbent clay is attapulgite clay. 4.The process of claim 3 wherein said attapulgite clay has been dried toprovide a water content of said clay within the range of 1-5 wt. %. 5.The process of claim 1 wherein said antimony pentoxide is supportedpredominantly within the internal pore volume of said porous absorbentsubstrate.
 6. The process of claim 5 wherein at least 80% of the surfacearea of said absorbent substrate is contained within the internal porevolume of said absorbent substrate.
 7. The process of claim 6 whereinsaid purified hydrocarbon product has a copper content of no more than0.03 ppm.
 8. An absorbent material composition effective for the removalof metal contaminants from a hydrocarbon product comprising: (a) aparticulate porous absorbent substrate material having an averageparticle size within the range of 1-5 mm; and (b) antimony pentoxidesupported on said absorbent substrate in an amount within the range of5-20 wt. % of said substrate and deposited predominantly within theinternal pore volume of said absorbent substrate.
 9. The composition ofclaim 8 wherein said substrate material has an effective pore sizewithin the range of 5-12 Angstroms.
 10. The composition of claim 8wherein at least 80% of the surface area of said absorbent substrate iscontained within the internal pore volume thereof.
 11. The compositionof claim 10 wherein said porous absorbent substrate has an average porevolume within the range of 0.7-0.85 cubic centimeters per gram.
 12. Thecomposition of claim 11 wherein said absorbent substrate material is anabsorbent clay.
 13. The composition of claim 12 wherein said absorbentis attapulgite clay.
 14. The composition of claim 13 wherein saidantimony pentoxide is supported on said attapulgite clay in an amountwithin the range of 10-15 wt. % of said clay.
 15. A process for thepreparation of an antimony pentoxide promoted absorbent comprising: (a)providing a particulate porous absorbent substrate having an averageparticle size within the range of 1-5 mm and an average effective porevolume within the range of 0.7-0.85 cubic centimeters per gram; (b)providing an aqueous dispersion of hydrous antimony pentoxide; (c)mixing said absorbent support with a portion of said antimony pentoxidesolution in an amount sufficient to prepare a mixture thereof and fillthe pore volume of the particulate porous substrate with said antimonypentoxide solution; (d) agitating said mixture of said particulateabsorbent substrate and said antimony pentoxide solution to effectdistribution of antimony pentoxide within the pore volume of saidsupport; and (e) thereafter drying said absorbent substrate promotedwith antimony pentoxide at a temperature sufficient to dehydrate saidsubstrate.
 16. The process of claim 15 wherein said antimony pentoxidesolution is mixed with said absorbent support in a plurality oftreatments in which, subsequent to agitating said mixture as set forthin subparagraph (b) and prior to drying said absorbent substrate as setforth in paragraph (e), the absorbent support material is mixed with atleast one additional portion of an aqueous solution of antimonypentoxide in an amount to fill at least partially the pore volume of theparticulate substrate with said antimony pentoxide solution andthereafter, subsequent to said additional mixing of said supportmaterial, agitating the mixture of said absorbent support material andantimony pentoxide solution to effect distribution of the antimonypentoxide solution within the pore volume of said support.
 17. Theprocess of claim 15 wherein said aqueous dispersion of antimonypentoxide has an antimony pentoxide concentration of at least 10 wt. %.18. The process of claim 17 wherein said absorbent substrate isattapulgite clay.
 19. The process of claim 18 wherein said attapulgiteclay has a water content within the range of 1-5 wt. %.
 20. In a processfor the preparation of a promoted absorbent effective for the removal ofmetal contaminants from a hydrocarbon product comprising: (a) providinga particulate porous absorbent substrate having an average particle sizewithin the range of 1-5 mm and an average of effective pore volumewithin the range of 0.75-0.8 cubic centimeters per gram with at least80% of the surface area of said support contained within the internalpore volume of said absorbent support. (b) providing an aqueousdispersion-of an absorption-promoting agent; (c) providing a mixture ofsaid absorbent substrate with said aqueous solution of promoting agentin an amount to at least partially fill the internal pore volume of saidabsorbent substrate with said aqueous solution of promoting agent; (d)agitating said mixture of said particulate absorbent substrate and saidaqueous solution of promoting agent for a time sufficient to effectdistribution of said promoting agent within the internal pore volume ofsaid absorbent support material; (e) thereafter contacting saidabsorbent support substrate with an aqueous solution of said promotingagent in an amount when added to the aqueous solution of promoting agentapplied in subparagraph (c) to provide an amount of the said aqueoussolution of promoting agent which is at least equal to the pore volumeof said porous absorbent substrate; and (f) thereafter agitating saidmixture of said particulate absorbent substrate and said aqueoussolution of promoting agent for a time sufficient to effect distributionof said promoting agent within the internal pore volume of saidabsorbent support material; and (g) thereafter drying said absorbentsubstrate material at a temperature sufficient to dehydrate saidsubstrate material with said promoting agent in place.
 21. The method ofsaid 20 wherein said promoting agent is an oxide of a metal selectedfrom the group consisting of arsenic, antimony, and bismuth.
 22. Themethod of claim 21 wherein said metal is antimony.
 23. The method ofclaim 22 wherein said promoting agent is antimony pentoxide.
 24. Themethod of claim 21 wherein said absorbent material is an absorbent clay.25. The method of claim 24 wherein said absorbent clay is attapulgiteclay.
 26. The method of claim 25 wherein said attapulgite clay has beendehydrated to provide a water content within the range of 1-5 wt. % ofsaid clay.